Machine-switching telephone system



r S. B. WILLIAMS, JR. MACHINE SWITCHING TELEPHONE SYSTEM.

APPLICATION FILED OCT. 10, 1917- Z Patented May 25,1920.

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S. B. WILLIAMS, JR.

MACHINE SWITCHING TELEPHONE SYSTEM.

APPLICATION FILED OCT. 10. 1917.

1,340,997, v Patented May 25,1920.

3 SHEETSSHEET 2.

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s. B. WILLIAMSIJR. MACHINE SWITCHING TELEPH'C'NE SYSTEM.

APPLICATION FILED OCT. IO, I9I7- I 1,340,997, Patented May 25, 1920.

3SHEETS-SHEET 3.

UNETED SKATES sarsur OFFlCE.

SAMUEL B. WILLIAMS, JR, 0F BRGQKLYN, NEW YORK, ASSIGNGR TO WESTERN ELECTRIC COMPANY, ING GRPORATED, NEW] YORK, N. 55., A CORPORATION OF NEW YORK.-

MACHINE-SWITCI-IING TELEPHONE SYSTEM.

essence.

Specification of Letters Patent.

Patented May 25, 1920.

To aZZ whom it may concern:

Be it known that I, SAMUEL B. lVILLmMs, Jr.,a citizen of the United States, residing at Brooklyn, in the county of kings and State of New York, have invented certain new and useful Improvements in Machine- Switching Telephone Systems, of which the following is a full, clear, concise, and exact description.

This invention relates to machine switch ing telephone systems and has for an object the prevention of false setting or actuation of selective switches through the accidental transmission of a single impulse.

It has often happened that a subscriber by carelessly handling his telephone instrument has so jarred or moved his switchhook as to cause a momentary break in his line circuit, thereby transmitting an impulse similar to one caused by the proper manipulation of the dial switch. If this happens just after the line switch or line finder switch has functioned or after selector switch has seized a trunk leading to another selector switch it results in the establishment of 1 wrongconnection, since the next selector will be actuated to set its brushes on the first group of contacts.

In certain commercial automatic telephone systems, another unstandard condition often arises whereby a subscribers bell is rung when, as a matter of fact, no conion was intentionally extended to his This is due to the fact that a subscriber has established partial connection and has ahandoned the call before sending the last digit of the call number. In this case a connector switch has been actuated in its primary movement only. If now the (all is abandoned, a single impulse to actuate the connector switch in its secondary movement will be transmitted before the relcusi mechanism can come into play, with the result that the brushes of the connector switch are set on the terminals ofthe first line of the selected group and very often ringing current will be momentarily transmitted to that line before the brushes are removed. Such an nil-standard condition is a source of great annoyance to the subscribers and a scheme for its prevention constitutes a useful improvement in the art.

iicccrdingly a feature of the present invention is the provision of means for alosorbing a single impulse which would ordinarily actuate a selective switch in its directed movement. According to this feature the impulse mechanism for setting the switches in such a system is arranged to send an extra impulse in each series of impulses, representing the characters of the designation of :1 called line, and means are provided to render such extra impulse in effective.

The drawings are a diagrammatic representation of a telephone system embodying the present invention. Figure 1 represents a calling subscribers line and a line finder switch; Fig. 2, placed to the right of Fig. 1, represents the connection extended to a selector switch; and 3, placed to the right of Fig. 2, represents the connection. extended to a connector switch and thence to a called subscribers line. Fig. 4% shows an alternative arrangement of relays used in Fig. 8 for carrying out the object of this invention.

The invention will be more readily understood from a detailed description of the operation.

Upon the removal of the receiver at substation A, line relay 100 is energized. In attracting its left armature it creates a calling condition upon the multiple 101 of substation A in the finders in which such line appears. In attracting its right armature, it energises relay 102 to start a line finder in search of the calling line. Belay 102, in attracting its upper armature, locks itself to conductor 103, independently of the right armature and back contact ofrelay 10st, and in attracting its lower armature, applies ground to multiple segment 105 individual to the group of lines to which substation A belongs, and also closes the circuit of the primary magnet PM of the line finder as of relay 1.02 also closes a circuit for relay;

114 to the escape magnet ESQ. At this time, however, the escape magnet does not operate, since it is shunted over the path traced, including the armature and back contact of magnet PM. Magnet PM energizes in the circuit traced and near the end of its stroke opens the shunt about the escape magnet, at which time the brush 114 is in contact with grounded group segment 105, and becomes energized over the following circuit: free pole of battery, magnet PM, magnet ESC, conductor 115, left armature and front contact of relay 111, conductor 116, brusl1114, segment 105, to ground at the lower armature and front contact of relay 102.- The escape magnet is constructed to release the side switch from position 1 to pcsition 2 upon'itsenergization. In position '2, the escape magnet is maintained energized over the following circuit: free pole of battery, magnet PM, magnet ESC, armature and back contact of relay 117, arm 118 and its second contact, conductor 119, con-v ductor 200, left armature and back contact of relay 202 toground. In position 2, arm 110 closes the following circuit for magnet SM to step the positioned finder brushes 120, 121, 122 over the multiples 123, 124 and 101, of the group to .which substation A belongs: free pole of battery, magnet SM, its armature and back contact, armature and contact of magnet'ESC, arm 110 and its second contact, conductor 109, to ground at the lower armature and front contact of relay 102. When the test brush 122 reaches the multiple 101 of substation A, the following circuit is closed to operate test relay 117 to stop the movement of the line finder: free pole of battery, resistance 125, left armature and front contact of relay 100, conductor 126,

multiple 101, brush 122, relay 117 to ground.

Relay 117 opens the circuit traced for magnet ESC, which becomes 'deenerglzed, and in retractmg its armature, opens the circuit of magnet SM to sto the finder on thecallin'g line terminals; l\ agnet ESQ, in deenergizing,freleases the side switch into position 3. In position 3 arm 118 energizes the cut-off relay 127 over the following circuit: free pole of battery,winding of relay 127, conductor 128,- contact 101, brush 122, arm 118 and its third contact, conductors 119, 200,

left armature and back contact of relay 202 to ground. Relay 127, ,in operating,"deenergizes relay 100. The retraction of the left armature of relay 100 removes the calling condition from multiples 101 of substation A, and the retraction of the right armature deenergizes relay 102. Relay 102, in repulse relay 131: free pole of battery, right winding of relay 131, conductor 132, arm 133 and its third'contact, conductor 134, arm 135 and its third contact, brush 121, terminal 124, through the telephonic apparatus at substation A, terminal 123, brush 120, arm 136 and its third contact, conductors 137, 138, left winding of relay 131, ground. Relay 131, in operating, energizes a slow release relay 139. Relay 139, in attracting its right armature, interposes a break in the circuit of finder release magnet RM. In attracting its left armature, this relay closes the following circuit to energize a slow release relay 202 (Fig. 2) ground, left armature, and front contact, of relay 139, conductors 140, 203, first selector side-switch arm 205, relay'202, free pole of battery. Relay 202, in attracting its left armature, closes the following circuit for relay 206, which, in operating, connects the primary magnet PM' to the back contact of the stepping relay 131: left armature and front contact 'of relay 202, conductor 261, right armature ductor 232, winding of relay 206, to free pole of battery.

hen the finder side switch moves into position 3, a distinctive tone istransmitted over the following circuit, to the calling line to indicate to the calling party that the central office apparatus is ready to receive im pulses: free pole of battery, secondary winding 223 of tone source 224, relay 218, conductor 222, left armature and back contact of relay 221, conductor 220, arm 219 and its first contact, armature and back contact of relay 209, conductor 225, right winding of relay 208, free pole of battery. This tone is transmitted by induction through the windings of relay 208 to the calling line over the following circuit; ground, left winding of relay 208, conductor 245, upper talking conductor 22 7,'condenser 269, conductor 137, arm 130 and its third contact, brush 120, terminal 123, through the telephonic apparatus at substation A, terminal 124, brush 121, arm 135 and its third contact, conducisarranged to transmit one more impulse in each case than is necessary for the proper setting of the switches. I

Upon the first retraction of the armature of relay 131 an impulse is transmitted over the following path: ground, primary oilnormal contact POE, armature and back contact of relay 131, right armature and front contact of relay 139, arm 1&2 and its third contact, conductor 1&3, conductor 207, winding of relay 2'72, to free pole of battery. Belay 272 is energized in this circuit and pre' 'iares a circuit for the transmission of the succeeding proper number of impulses to the stepping magnet. Upon the attraction of the armature of relay- 272 a circuit, including relay 273, is established from ground, winding of relay 273, front contact and armature of relay 272, winding of relay 272, to free pole of battery, but this circuit is ineffective in energizing the relay 273, as long as the armature of relay 181 rests on its back contact. Upon the next energization of relay 131, and the removal of the ground that shunts relay 27 3, this circuit becomes ciiectiye and relay 273 thereupon attracts its armatures. Upon each succeeding retraction of the armature of relay 131 an impulse is transmitted from the armature, bacl'r eontact of relay 131, over the circuit described, to the armature and front contact of relay 278, thence to the back contact and lefthand armature of relay 208, slow release relay 209, arm 210 and its first contact, conductor 211, letit armature and front contact I of relay 206, magnet PM, to free pole of battery. Magnet PM in response to these impulses steps the selector brushes 212, 213 and 21 i into operative relation with the de sired roup oi trunks containing the trunk to 215, 216 and 217.

In Fig. i there is shown a modification of the means for absorbmg the first impulse.

In this scheme relay 27315 replaced by a relay 27 S which instead of being slow to release is provided with a double winding, the operating result in each case being the same. It should be noted that while the armature of relay 272 is attracted the circuit through relay 273 or through the right. Winding of relay 273 is sulhcient to hold the relay 273 or 273 energizethbut is insufficient to hold the relay 27 2 energized. During the trans mission of the impulses, relay 272 is 311.81? gized only while the armature of relay 131 is in connection with its back contact, but, being slow to release, it holds its ar .ature attracted until. after the impulses cease. Also, during the sending of these impulses relay 273 andthe right winding of relay 27" is shunted during the same intervals.

In the case of relay 27 it being slow to release will holdits armature attracted until after the whole series of impulses has been transmitted. In the case of relay 2753", the

ground.

the right winding is shuntedthe left winding will be energized and hence the relay will hold its armature attracted until all of the impulses have been transmitted.

Relay 209, being slow to release itsarma ture, is maintained energized during the transmission of the impulses. In attracting its armature, this relay closes the following circuit for a relay 218: ground, armature and front contact of relay 209, arm 219 and its first contact, conductor 220, left armature and back contact of relay 221, conductor 222, relay 218, secondary winding of tone source 22%, free pole of battery. Relay 218, in operating, closes the following circuit for the escape magnet 228 of the first selector, which magnet is constructed to release the side switch from position to position upon its deenergization: free pole of battery, magnet 228, arm 229, conductor 2457, spring 2% and armature of relay 18 to ground. V lVhen the sender S restores and maintains relay 131 energizes, relays 272, 273 and 209, atter a slight interval, become de'c'energized, the latter opening the circuit of relay 218, which, in de energizing, opens the circuit of the escape magnet 228, which, in releasing its armatures, passes the side switch to position 2. to initiate the trunk hunting operation. In position 2, escape magnet 228 is again ener gized over the following circuit: free pole of battery, magnet 228. arm 229 and its second contact, spring 230, now closed to its lower contact, to ground. Magnet 228, in attracting its armature, closes a selfinterrupting circuit for the secondary stepping. magnet SM of the first selector: free pole of battery, magnet SM, its armature I and back contact, armature'and front contact of magnet 228, arm 231, conductor 232, left armature and back contact of first selectorrelease magnet RM armature and back contact of relay 221, conductor 261, left armature and front contactof relay 202 to Magnet SM thus steps brushes 212, 213 and 21-1 over the selected group in search of an idle trunk; Test multiples 217 of busy trunks are grounded, as will hereinafter appear. Upon the'first secondary step of the brushes, contact is opened and the escape magnet is dependent for its 7 continued energization upon the grounded test terminals 217 of busy trunks. When the first idle trunk is reached, the ungrounded condition of its test multiple 217 causes the deenergization of the escape mag net, which opens the stepping circuit, thus stopping the selector upon such trunk and in deenergizing passes the side switch to position 3. y

In position 3 ground is. supplied to the test multiples 217 of the Seized trunk over the'following circuit: brush 214:, conductor 236, arm 237 and its third contact, right armature and front .contact of relay 202 to ground. The application of this ground energizes a relay 300 in the connector (Fig. 3), which, in attracting its outer right arma-- ture, :connectsprimary magnet PM of the connector to the upper talking conductor 301 to receive the tens impulses, and inattracting its left xarmature, interposes a break in the circuit of the connector release magnet R M The calling party now operates 'hissender S to transmit 'thetens digit of the wanted number. I 7

' Upon the first retraction of the armature of stepping relay 131 the'relay 272 is energized,as before described, to prepare a circuit" for thesucceeding proper number of impulses. ..Upon the next attraction of the armature of stepping-relay'131, relay 273 or273, as the case: may be,is energizedand upon 'each succeeding retraction of the armature of thestepping relay. 131, an impulse is transmitted over the following circuit' to the primary steppingmagnet P?M of the connector: armature of relay 131, now grounded, and its back contact, right armature and front contact of relay 139,

arm 1 12and its" third contact, conductors 143, 207, armature and front contact of 273, left armature and back contact of relay 208, relay 209, arm 210 and its third contact, conductors 243, 1 15, arm 146 and its third contact, conductors 1 17 and 235, brush 212,. terminal 215, conductors 301,

302, outerarmature and front contactof relay 300, arm 303 and its first contact, magnet P M free pole of battery. Magnet P M thussteps the brushes 304C, 3 05, 306 into operative relation with the group of terminals containing those of the wanted I line307, 308 and 309. The slow release relay 209 in the circuit traced for the primary magnet remained energized during thetrans missionof the impulses. In attracting its armature, this relay closes the following circuit for the escape magnet 3100f the con- .nector which releases the connector side net 310, free pole of battery. 'VVhen the sender restores and maintains impulse relay 131 energized, the slow relay 209, after a slight interval, becomes Iinert, opening the circuitftraced' for the escape magnet 310, wh1ch,11n releasing its armatures,passes the connector sideswltch to position 2.

' In position 2, arm, 303 substitutes the secondary magnet S M for the primary magnet P M in the stepping circuit. The calling party now operates his sender S to transmit the unit digit of the wanted number. Upon the first retraction of the armature of relay 131, relay 272 is energized, as before described. Upon the next attraction of the armature of relay 131, the

' connector escape magnet 310 over sidesw itch arm 313, now by way of its second contact. The magnet M steps the brushes 304;, 305, 306 into engagement with the multiples, 307, 308 and 309 of the desired line. If the line is busy its test terminal 309 will be'grounded' over a brush 306, arm, 316 and its third contact, and the, left grounded armature of the relay 315, or such arm ,and'its fourth contact and the righthand low-resistance winding of the relay 315 to ground of. some other connector switch. In such event, the left-hand highresistance winding of relay 315 of the testing connector is fshunted and the relay does not attract its armatures. .In passing out of position 2, connector sideswitch arm 317 opens the circuit of relay 300. This relay thereupon becomes inert, and in retracting its left armature, closes the circuit of connector release magnetR M as follows: free pole of battery, magnet R M conductor 318, left armature and back contactof relay 300, primary off-normal contact 319 to ground. The release magnet in energizing restores the connector to its nor- '-mal position and also restores the side switch. Before contact 319 opens, hoW-' ever, as the brush shaft is restored, contact 320 closes, which results in a locking circuit being provided for magnet RPM as follows: free pole of battery, magnet R M left armature and back contact of relay 300, conductor 321,. contact 320,. resistance 322', conductor 323, right .armature and front contact of magnet R M release conductor 325, terminal 217, brush 2141, conductor 236, arm 237 and its third contact,

right armature and front contact of relay 202 to ground; Magnet R M at its .left

armature and front contact, closes the following circuit to produce a busy tone in the calling line to indicate to the calling party that the line desired is occupied: ground, secondary winding of source of busy tone current 326, left armature and front contact of magnet R M arm 327 and its first contact, condenser 328, arm 329 and its first contact, conductors 330 and 311, terstores the side switch.

ininal 216, brush 21 3, conductors 239, 150, arm 14:9 and its third contact, conductors 1-18 and 23.8, arm 219 and its third contact, armature and back contact of relay 209, conductor 225, right winding of relay 208, free pole of battery. An induced current is created in the secondary winding of relay 208 included in the calling circuit. This circuit is the same as that traced for the dial tone. The calling party, upon hearing this busy tone, replaces his receiver. The replacement of the receiver decnergizes relay 131, which in retracting its armature, opens the circuit of slow relay 139. This relay after a slight interval releases its armatures, the retraction of the right armature closing the circuit of finder release magnet as follows: free pole of battery, magnet RM, conductor 151, right armature and back contact of relay 111, conductor 152, right armature and back contacts of relays 139, 131, contact PON to ground. The release magnet, in addition to restoring the finder brush shaft 153, also restores the side switch. The retraction of the left armature of relay 139 deenergizes relay 2,02. Relay 202, in retracting its left armature, opens the circuit of relay 206., which relay, in retracting its right armature, closes the circuit of first selector release magnet RM as follows: free pole of battery,'magnet R M right armature and back contact of relay 206, contact PON, to ground. Magnet RM', in addition to restoring the selector brush shaft, also re- WVhen the shaft reaches its normal position, contact PON opens and deenergizes the magnet RM. The retraction of the right armature of relay 202 removes ground from conductor 236, which resultsin the .deenergization of connector release magnet R 11 The apparatus is now all restored.

Assuming the selected line to be idle, full potential is present upon the multiple 309 thereof, and the test relay 315 becomes energ-ized over its left -hand high resistance winding in the third position of the side switch. This circuit is as follows: ground, left .windingof relay .315, arm 316 and its third contact, brush 306, terminal 309, outoff relay of the selected iline, free pole of battery. Both the cut-50.1 relay and the relay 315 become energized in this circuit, the former removing thecontrol of the line relay from the selected line inthe well-known manner, and the latter connecting the test multiples 30 9 directly to ground over its left armature to cause the selected line to test busy to other connectors. The attraction of the right armature of relay 315 energizes a slow relay 331 over the following circuit: free pole of battery, relay33-1,-arm 332 and its third contact, right armature and front Contact .ofrelay 315, right-hand low resist ance winding of relay 315, to ground. Relay 331, in attracting its armature, closes a locking circuit for relay 300 as follows: free pole of battery, relay 300, its inner right armatureand front contact, conductor 333, right armature and front contact of relay 331'to the grounded third wire 325. This circuit is closed before the circuit in cluding the arm 317 and its second contact is opened, as the side switch passes out of position 2. Thus the relay 300- holds its left armature attracted to maintain the connector release circuit open. In parallel with the relay 331, the escape magnet 310 is energized to apply ringing current to the selected line. The ringing circuit is as follows: free pole of generator 334:, ringing cut-off relay 31-1, inner armature and front contact of magnet 310, arm 335 and its third contact, brush 305, terminal 308, bell 336, terminal 307, brush 30 1, arm 337 and its third contact, outer armature and front contact of magnet 310, to ground A portion of the ringing current flows over the following circuit to indicate by a characteristic tone to the calling party that the selected line is being signaled: free pole of generator 334:, relay 314C, inner armature and front contact of magnet 310, conductor 338, arm 327 and its third contact, condenser 328, arm 329 and its third contact, conductors 330, 311, terminal 216, brush 213, conductors 239, 150, arm 149 and its third contact, .conductors 1&8, 238, arm 219 and its third contact, armature and back contact of relay 209, right-hand winding of relay 208, free pole -of battery. This tone is transmitted by induction, through the windings of relay .208 to thecalling line, as before described.

When the called party removes his receiver, marginal ringing cut-off relay 314 becomes energized, opening the circuit of escape magnet 310 which, in deenergizing, passes the side switch to position 4. In position 4 arm 316connects the test multiples 309 to ground through the low resistance right-hand winding of test relay 315 to maintain such line busy. Arm 332 in passing out of position 3, opens the circuit of slow relay 331. Before this relay retracts its right armature, however, arm 317 reaches position 4: and connects release relay 300 to the groundedthird conductor 325 to prevent premature release. The arm 329 reaches its fourth contact before the left armature of relay 331 is retracted, which results in an impulse being transmitted over the following circuit to energizethe called supervisory relay 208: ground, left armature and front contact of relay 331, arm 329 .andits fourth contact, conductors 330. 311, terminal 216, brush 213, conductors 23,9, 150, arm 14:9 and its third contact, conductors 148, 23.8, arm 219 and its third contact,armature and back Contact of relay 209; conductor right When the impulse ceases and relay 208 re-.

tracts its right armature, the escape magnet in releasing its armatures, passes the side switch to position 4, in which position the called supervisory relay 208 is energized over i the called line circuit asfollows: free pole of battery, right winding of relay 208, conductor 225, lower armature and back contact of relay 209, arm 219 and its fourth contact, conductors 238, 148', arm 149 and its third contact, conductors 150, 239, brush 213, terminal 216, conductor 311, arm 335 and its fourth contact, brush 305, terminal 308, through the telephonic apparatus at substation B, terminal 307, brush 304, arm 337 and its fourth contact, conductor 301, terminal 215, brush 212, conductors 235, 147, arm 146 and its third contact, conductors 145, 243, arm 210 and its fourth contact, arm 244 and its fourth contact, conductor 245, left winding of relay 208, to ground. Relay 208 in holding its left armature attracted, permanently interposes a break in the impulse circuit to prevent the calling party from thereafter transmitting impulses to the magnets, and in holding its right armature attracted, closes ,a substitute circuit for slow relay 202 as follows: ground, right armature and front contact of relay 208, conductor 246, arm 205 and its fourth contact, re-' lay 202, free poleof battery. Since relay 202 controls the release of the first selector and connector as described, the release of these switches is now controlled by the called party. The parties may now converse, talking current being supplied to the calling line over the windings of relay 131 and to the called line over the windings of relay 208.

Upon the termination of the conversation and the replacement of the receiver by the calling party, the finder is released as already desoribed. The replacement of the receiver by the called party deenergizes relay 208, which, in retracting its right armature, opens the circuit of relay 202. Theretraction of the left armature of this relay deenergizes relay 206 as described in connection with a busy call, the deenergization of this relay causing the release of the first selector; The retraction of the right armature of relay 202 removes ground from the third wire 236, with the result that relay 300 becomes inert, and at its left armature and back contact closes the circuit of release magnet R M of the connector as described in connection with a busy call. 1

Other features,inluding the passing of part of the the finder side-switch arms into the fourth position under certain conditions, form no present invention and will not be described.

What is claimed is:

1. In a telephone system, telephone lines, a plurality of selective switches for interconnecting said lines, means for sending impulses, a circuit for the transmission of said impulses, means responsive to the initial successive presence and absence of flow of current over said impulse circuit for extending said circuit to one of said switches, and means for operating said switch, said extending means being responsive to a second successive presence and absence of flow of current over said impulse circuit after the operation of said switch to extend said circuit to an additional one of said selective switches.

"In a telephone system, telephone lines, a plurality of selective switches for interconnecting said lines, means for sending impulses, a circuit for the transmission of said impulses, means responsive to the cessation of a single impulse transmitted into said circuit for extending said circuit to one of said switches, and means for operating said switch, said extending means being responsive to the cessation of a single impulse subsequent to he operation of said switch to extend said circuit to an additional one of said selective switches.

3. In a telephone system, telephone lines, selective switches for interconnecting said lines, a circuit for the transmission of impulses, means for extending said circuit to said switches responsive to the transmission and cessation of'a single impulse over said circuit, and means for maintaining said extended circuit continuous during the continued transmission of like impulses;

4. In a telephone system, telephone lines,

selective switches for interconnecting said lines, actuating means responsive to current impulses for moving said switches to their successive'operative positions, a calling device for sending series of impulses tosaid actuating means, said device being arranged to send an extra impulse in each seriesadditional to those required to operate said actuating means, and means including a relay for rendering ineffective said extra impulse. i

5. Ina telephone system, telephone lines, selective switches for interconnecting said lines, means including calling devices for setting said switches, each said calling device being arranged to send one more impulse than is necessary for the proper setting of said switches, a relay arranged to be energized by said impulses, a circuit arrangedtobe closed by said relay,;a second relay included in said circuit and arranged to be shunted by said means for setting said switches and energized in series with said first relay, a circuit for the transmission of impulses to said switches controlled by said second relay, and means for keeping both said relays continuously energized during the further transmission of said impulses.

6. In a telephone'system, telephone lines, selective switches for interconnecting said lines, calling devices for setting said switches, each arranged to send one more impulse than is necessary for the proper set ting of said switches, a pair of relays for preparing and maintaining a circuit for the transmission of impulses to said switches, said relays being arranged to close said circuit at the end of the first impulse from said calling devices. i a

7. In a telephone systeni, telephone lines, selector switches for interconnecting said lines, a primary impulse circuit, a second ary impulse circuit, means responsive to changes of the flow of current in said primary circuit for changing the flow of current in said secondary circuit, means responsive to the initial successive presence, absence and presence of flow of current in said primary circuit forextending said secondary circuit to'said switches, and means responsive to the next absence of flow of current in said primary circuit for causing said switch to take a single step.

8; In a telephone system, telephone lines,

selective switches for interconnecting said lines, a line relay for producing impulses, a normally open circult for the transmission of said impulses, means operated upon the successive energization, denergization and energization of said relay to partially close said impulse circuit, and means operated upon the next deenergization of said relay to complete the closure of said circuit.

In witness wl'lereof I hereunto subscribe my name this 4th day of October A. D., 1917.

SAMUEL B. WVILLIAMS, JR. 

